General Description

ABS EQUIPPED
This vehicle has an antilock brake system (ABS) which controls the front and rear disc brakes to minimize wheel lockup during heavy braking on most road surfaces. The ABS utilizes a diagonally split master cylinder and tandem power booster, which are similar to those used in non-antilock systems. The system also includes a pressure modulator valve assembly, electronic brake control module (electronic brake and traction control module, on vehicles equipped with traction control), wheel speed sensors, and rear-mounted proportioner valves.

DIAGONAL SPLIT SYSTEM
Using a conventional diagonally split brake system plus an ABS unit, the brake system operates normally while the ABS monitors wheel speeds and brake pedal position. The conventional system will continue to operate normally until the control module detects a wheel beginning to lock up or the brake pedal traveling beyond a specified limit. When either of these conditions exists, the brake system switches from a normal, conventional braking mode to the antilock mode. The ABS will then remain in control of the system until braking is no longer occurring, or the wheel locking and for excess pedal condition no longer exists.

MODES OF OPERATION
Brake pedal operation and feel during normal braking is like that of a conventional vacuum-boost brake system. However, when the system is in the antilock mode, a series of rapid pulsations might be felt in the pedal, and the pedal might even rise a little. This is normal and should not be of concern.

ABS CHARACTERISTICS
Characteristics of the brake system while operating in the antilock mode include a ticking or slight popping noise which might be heard coming from the pressure modulator valve assembly. Initialization of the (ABS) pump may be heard at approximately 10 km/h (6 mph). During antilock braking on dry pavement, the tires may make intermittent chirping noises as the wheel(s) approach lockup. Some vehicles are also equipped with a traction control system (TCS), which is designed to prevent wheels from spinning excessively during acceleration.

ABS VS TCS
The system operates at all vehicle speeds, and reduces wheel slip by braking the wheel which is losing traction. A primary difference between the traction control mode and the antilock braking mode is that brake fluid pressure is increased to lessen wheel spin during traction control, but is reduced during antilock braking to enable greater wheel spin. A normal characteristic of traction control system may include an initialization noise at approximately 20 km/h (12 mph). The ABS and TCS share many of the same components in the hydraulic and electrical systems.